I’m not familiar with what this for loop is actually doing. Would anyone be able to explain? https://elixir.bootlin.com/linux/v5.10.75/source/kernel/sched/rt.c#L621 Answer This macro is setting rt_se to NULL after the instructions block that follows has been executed. The use of such “access”…
Tag: scheduler
Linux: Why does the FIFO scheduler not work as expected on the 1 core CPU machine?
I am learning about Linux scheduler. Firstly, I want to test the FIFO scheduler. Here is the code I use to test: I run this program with the priority 1 on 2 terminals: ./main 1. Because my CPU has only 1 core, I expect only the first terminal can run because of the FIFO attribute. However, in the real-test si…
Can process move from Ready Queue to Job Queue?
I’m working on a program that would simulate scheduling from creation to completion of processes. I need assistance to know can a process move back from ready queue to the job queue (in any case – may be an exception). Answer I’m not sure what you mean by “queue job”. A process i…
Linux default scheduler alternatives
The Linux kernel implements the Completely Fair Scheduling (SCHED_NORMAL) algorithm as its default scheduling algorithm for scheduling real-time processes. How to modify the linux kernel such that the default scheduling policy is set to round-robin (SCHED_RR) or any other scheduling policy ? Is there a generi…
How can I write a I/O bound C program?
I must write programs that are I/O Bound and that will make my I/O scheduler work like never done before for a Operating Systems homework, but I have no idea how to do it. I’ve tried writing a simple C program that counts the lines of big text files, but it executes too fast and I can’t measure th…
Linux context switch internals: What happens when process exits before timer interrupt?
How is context switch made in linux kernel when process exits before timer interrupt? I know that if the process is running and timer interrupt occurs then schedule function is called automatically if the flag is set, schedule function then selects next process to run. Basically in this case the schedule func…
Completely Fair Scheduler (CFS): vruntime of long running processes
If vruntime is counted since creation of a process how come such a process even gets a processor if it is competing with a newly created processor-bound process which is younger let say by days? As I’ve read the rule is simple: pick the leftmost leaf which is a process with the lowest runtime. Thanks! A…
Linux SCHED_OTHER, SCHED_FIFO and SCHED_RR – differences
Can someone explain the differences between SCHED_OTHER, SCHED_FIFO and SCHED_RR? Thanks Answer SCHED_FIFO and SCHED_RR are so called “real-time” policies. They implement the fixed-priority real-time scheduling specified by the POSIX standard. Tasks with these policies preempt every other task, wh…